


Animosity

by 0neType



Category: Undertale (Video Game)
Genre: Alternate Universe - Underswap, Blackrom, Blow Jobs, Light Bondage, M/M, Riding, Rival Sex, Rivalry
Language: English
Status: Completed
Published: 2017-01-25
Updated: 2017-01-25
Packaged: 2018-09-19 23:15:18
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,102
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9464825
Author URL: https://archiveofourown.org/users/0neType/pseuds/0neType
Summary: Sans is fairly certain he'd qualify as a nice, decent sorta guy byanyone'sstandards.It's just that there's something about Edge that pushes all the wrong buttons.





	

**Author's Note:**

> oh man, i've had a craving for blackrom edgeberry for literal MONTHS
> 
> idk how to explain this to u guys but to say that this is incredibly self-indulgent lmfaooo i'm sorry for all the headcanons i probably destroy in the characterization of these two here hhhhhhhhhhhHHHHH

Sans pushed Edge hard into the room, watching the taller skeleton chuckle even as he stumbled backwards. He frowned at him and glanced out into the hall to make sure they were still alone before locking the door behind them. That done, Sans turned back around to face the sharp-angled monster now lounging on his bed.

“I see you have very… specific tastes.” The skeleton smirked at him, running his phalanges over the frame of his rocket ship bed.

Sans flushed, a building irritation making him frown at the same time, “Anyone ever tell you what a jerk you are?”

“All the time.” Edge said as he lay down flat on his back and placed his hands casually behind his skull, “Why? Are you upset that you didn’t have the privilege of being the first?”

Sans snorted, “As if.”

When Edge startled to cackle to himself at that, Sans only deigned to roll his eyelights at him before turning around again. He paused for a moment to consider what it was exactly he was doing before steeling himself and proceeding to take his boots and his gloves off. His soul pounded harder as each piece was removed, his bones rattling ever so slightly in anticipation. But it was only as he was peeling the second glove off his hand that he felt a piercing stare at his back. Sans shot a glance over his shoulder to see Edge sitting upright in bed, positively _leering_ at him.

Sans felt the burn of his magic threaten to spark against his cheekbones in embarrassment. But he couldn’t stop now—losing nerve in front of the other skeleton was the absolute last thing he wanted to happen. So, he turned away quickly and ignored the way his phalanges trembled as he leaned over to carefully shift his boots to the side. All the while, he could still feel Edge’s gaze on him, not wavering for even a moment.

“Pervert.” He mumbled under his breath but apparently, it wasn’t low enough to go unheard because the other skeleton laughed loudly in response.

“How am _I_ the pervert when _you’re_ the one who brought me into his room and proceeded to strip?”

“I’m not _stripping_.” Sans groused, turning around fully to face the monster sitting easily on his bed and resisting the absurd urge to stomp his foot in indignation.

“Really?” Edge said, his voice going low and sultry as he caught Sans’ gaze and held it, “Well, that’s disappointing.”

The tone of it made him shiver and Sans didn’t even need the little huff of laughter from Edge to know that his face must have gone bright with the rich blue of his magic once again. He could feel the heat of it warming against his bones, tingling wherever it blossomed. Then, when Edge shifted a little where he sat, spreading his femurs open a touch wider, Sans could practically taste the resulting pulse of his soul on his tongue. The magic flowed from it and painted onto his bones, cyan stark in the dimly lit room.

“And here I thought that you brought me in here with something in mind.” The taller skeleton finished, phalanges brushing invitingly against the slightest hint of red that was glowing at the front of his dark, black uniform pants.

From that simple gesture alone, Sans felt his own magic respond in kind, redirecting downwards with embarrassing speed. It swirled and coiled at his pelvis, unshaped but eager to form. Sans pushed down his inner mortification as Edge’s eyelights flickered towards it and the sharp curve of a smug smile worked its way onto his face at the sight.

Instead, Sans did his best to puff out his chest a little and use the moment of distraction to stride as confidently as he could towards the relentlessly teasing monster.

“Well, I suppose you’re not _entirely_ wrong.” He said, faking all the confidence he felt he should have and blushing a little brighter when his voice came lower and much more whispered than he intended.

Edge raised a browbone at the tone of it, an infinitely amused look casting onto his features. He opened his mouth—to say something scathing and rude, no doubt—but Sans refused to let him finish. He leaned down close and knocked his closed teeth at Edge’s own mouth, startling him into silence. Sans used the surprise to press further towards him, crawling into his lap and conjuring his tongue to slip into Edge’s still open mouth.

To the other monster’s credit, it didn’t take him very long to catch up. In fact, as Sans swiped his tongue along the inside planes of his hard bone, Edge quickly formed his own tongue to meet him. He followed it up with grabbing tightly onto Sans’ hips with both hands, gloved phalanges digging into the fabric of his pants and dragging roughly against his body.

Sans moaned into the kiss, the friction already addictive to his sensitive bones, tense from a whole day of ruthless teasing at the hands of the irritatingly sly monster. Just remembering the day’s events had Sans heating up further, desperately licking into the other skeleton with a wordless plea. Edge gripped tighter onto him in response, rocking his hips up and making Sans gasp as their pelvises rubbed up together.

Edge pulled back from him with a grin, “I see that you’re enjoying this.”

Sans barely managed to hold himself back from a frustrated groan as he glowered at him, “I’d enjoy it a lot _more_ if you could stop talking.”

“Unfortunately for you, I ‘love hearing the sound of my own voice.’” Edge quoted, calling back to Sans’ own taunts from earlier that day, “So, you’re shit out of luck, it would seem.”

Sans sighed with annoyance, glaring hard at the other skeleton. He’d had more than enough of being frustrated and embarrassed today. More to the point, he’d had enough of butting heads with his brother’s alternate over every, single, tiny little thing. It didn’t seem fair to him that there was so much friction between the two of them when his _own_ twin and Papy got along so well. Surely the sparks between him and Edge could translate into something a little more pleasurable?

He didn’t think it was too much to ask that at least _this_ would go smoothly between them.

“Don’t you think you’re underestimating me a little?” Sans said, pushing at Edge’s chest and knocking him flat onto his back before moving up a little further to pin his hands to the solid frame of his headboard.

The skeleton just looked up at him, amused, not even bothering to try and break free of his hold, “Not really.”

Sans grit his teeth.

There it was again. That _irritation_.

There was just something about his brother’s counterpart that set him on… well, _edge_.

Maybe it was the way that there was still so much different about them even though by all accounts they held the same ‘role’ in their respective universes. Or, maybe it was the fact that Edge—so prideful and self-aggrandizing—was already a Royal Guard when Sans was still struggling to get Alphys to take him seriously. Edge seemed to rack up accolade after accolade with the exact same skillset as Sans while he himself stayed right at the bottom rung of the ladder to success. Honestly speaking though, Sans didn’t think it made a difference whether it was jealousy or just incompatibility that sparked that agitation between them.

There was just something about Edge that brought out a rarely seen side of him; one that he hadn’t even known _existed_.

One that would _revel_ in knocking the other skeleton down a few pegs.

“Well,” Sans let a bright smile flicker onto his face and tugged roughly at Edge’s scarf till it came off in his hands, “Then I suppose you’ll have no one to blame but yourself for the consequences.”

Edge gave him a long look, confusion playing across his features, “… consequences?”

Sans ignored his questioning tone, instead leaning forward to capture both Edge’s slender wrists in one hand. He then used the deep, red scarf he’d ripped from around the skeleton’s neck to tie them together and subsequently back against the headboard. Throughout the whole process, Edge remained blissfully silent, scowl firming taking root on his face. When Sans finally leaned back with a satisfied sigh, his knots expertly holding their place, Edge simply looked bewildered.

“And how exactly is this meant to keep me from talking?”

“It’s not.” Sans grinned down at him, crawling forward till his clothed pelvis was mere inches away from Edge’s sharp teeth, “It’s only supposed to keep you from putting your hands where I don’t want them. Not yet anyway.”

Edge eyed him warily as he began to work off his pants, “Then…?”

Sans leaned down then, smirking wide and relishing in the apprehensive look on the other monster’s face before continuing on with all the zeal of trying out a new recipe, “I’ve got a few interesting ideas on how to keep you quiet. I think you’ll like them~”

There was something _immensely_ gratifying about the way Edge’s sockets widened at the sight of Sans’ working his dick out of his pants. The soft cyan glow of it reflected off the scarred planes of the skeleton’s face beneath him, and Sans couldn’t help but grin as Edge’s eyelights shrank to pinpoints as he caught up with the situation at hand. Immediately, the taller skeleton tried to buck Sans off of him, but Sans squeezed tight with his femurs and kept himself in place.

“You _cannot_ be serious.” Edge growled, trace hints of red starting to glow over his sharp cheekbones and betraying his embarrassment.

“Oh? Is there a problem?” Sans asked, mock innocent, resisting the sudden, inexplicable urge to rub his already leaking length against the other skeleton’s face in some sort of sadistic display of dominance, “I’d have thought that something like this would be no trouble at all for the _Great_ and _Terrible_ Papyrus.”

Edge didn’t respond, simply staring at him instead.

Sans stared back, “… what?”

“Just surprised, is all.” He said, his eyelights flashing, darkly entertained, “Guess you’re not as spineless as I thought you were.”

Before Sans could respond, Edge’s tongue flicked out and licked up the front of his erection in an instant, catching Sans off-guard. He barely managed to hold back a yelp, eyelights flickering out in surprise. Sans did his best to maintain his composure in light of the sudden attention, but his reaction didn’t go unnoticed by Edge. The skeleton’s chest rumbled with laughter even as he wrapped his mouth around the tip of Sans’ cock and slicked it with his spit. He sucked on the head—remarkably gently—before pulling off with a _pop_ and returning to lave at his length with renewed vigor.

“You…” Sans started, breaking off midway through his sentence as Edge carefully wrapped his mouth around him once more and bobbed his head as best as he could from his position, “Hah… _god_.”

Sans shivered above him, argument forgotten as the other skeleton continued to blow him. The wet, warm heat surrounding him felt amazing—so good that even when Edge’s sharp teeth caught periodically against his conjured flesh, the prickles of pain barely registered through the overall pleasure of it all. This time, when Edge sucked on his head before pulling off entirely, Sans couldn’t help but groan in desperation, hips rocking forward automatically.

Edge simply turned his head away, laughing again, “Now, remind me. What was your plan here exactly?”

The _plan_ had been to one-up Edge for a change—to be the one in charge, in control. It was clear now that his tactic had stupendously backfired. He hadn’t expected the other skeleton to be so skillful at something like _this_.

Clearly the dating manuals they each had in their respective universes had some heavy differences.

“So good I’ve left you speechless, hmm?” Edge snickered and Sans could feel the warm, fuzzy heat of pleasure give way to the sharp prickling of anger at his tone, “Funny. I thought _I_ was the one who was supposed to stop talking.”

“This isn’t working.” Sans mumbled, the haze in his mind clearing enough for him to rethink his strategy.

“What’s next?” Edge smirked up at him, “Gonna choke me on your dick to shut me up?”

The idea was tempting—the image of Edge gasping desperately around his length with tears streaming down his face jolting through him in a way that was wholly new and ridiculously arousing—but Sans was loathe to follow through on anything Edge suggested. If he did that, it wouldn’t matter if it worked; Edge would just take credit for the idea and Sans’ efforts would be for nothing. If he _really_ wanted to shut Edge up, he had to do it differently.

He had to do it in a way that would leave a permanent impression.

With a dawning idea and a slow smile, Sans slid down Edge’s body till he was sitting firmly on his lap. There was a meaningful glow there already, practically buzzing with magic ready to be put to use. The other skeleton frowned at him but didn’t do anything else, watching him carefully. Sans smiled at him again, a brilliant mega-watt stretch of a thing, no doubt dazzling in display.

It was gratifying to see the way Edge shrank back from it.

Reshaping magic once it had already formed in a surge of arousal was a difficult thing, but Sans had always been gifted with incredible prowess in the area. It didn’t take too much work on his part to switch up from his hard and leaking cock to an even wetter pussy, practically dripping down onto Edge’s pants beneath him. Sans near laughed at the expression on the other skeleton’s face, his eyelights focused on the pretty blue mound glowing invitingly at him.

He lets his phalanges drift down to the buckle of Edge’s pants, quickly undoing it and pulling the zipper down shortly after. When he reached in and gave the long, red cock resting there a tentative stroke, he was rewarded with a bitten back groan from the restrained monster in his bed. Sans grinned, pumping the length a few more times before dragging it out from the confines of the pants and sinking down to put it into his mouth.

“Shit!” Edge gasped, thrusting his hips up in an attempt to sink deeper. But Sans had been prepared for exactly that sort of outcome and he held Edge down while continuing to slick up his cock. He wrapped his tongue around it and sucked, bobbing roughly up and down while listening to the other skeleton try and fail to keep himself quiet.

With a grin, he popped off and stroked the now fully hard erection in his hand a few times, prepping it by spreading the wetness down the entire length of it. Then he adjusted himself till his was properly on top of Edge, knees bent on either side of his long, long femurs. Sans braced himself with one hand behind his back, lifting himself into the air while using the other to position Edge’s cock at his entrance.

“W-wait—”

Sans slammed himself down onto the thick, red cock, reveling in the way it felt and the way it made the other skeleton’s sentence break off into a breathless exhalation instead.

“ _Fuuuck_.” Edge groaned, throwing his head back with a pant and pulling on his restraints.

“L-language.” Sans chastised, forcing past his winded breath and the thudding of his soul in his ribcage as the cock inside him stretched him out more than he had originally expected.

It took him a moment to adjust, still relatively inexperienced with this sort of thing—not that he’d ever admit it to Edge—and uncertain about how best to proceed without hurting himself. Surprisingly enough, the other monster didn’t get impatient. In fact, he didn’t say a thing at all as Sans cautiously lifted his hips a few times to test out the few without actually doing much thrusting at all. It seemed as if Edge was far to preoccupied with trying to control his breathing, face flushed with magic and chest heaving already.

When Sans finally lifted himself up and sank slowly back down again, he was inordinately amused as the whimper it drew from the skeleton beneath him.

“You _like_ this.” He said, more a statement than an actual question.

Edge refused to look at him; refused to say anything at all. His face only glowed brighter as Sans repeated the motions, circling with his hips and letting Edge’s cock fill and empty him over and over.

“What? Nothing to say anymore, tough guy?” He teased, “I guess you’re not so ‘Great and Terrible’ after all~”

Edge’s eyelights flashed dangerously, “How _dare_ —”

Sans slammed his hips back down, Edge’s dick shifting fully into him and making them both groan out loud, Sans’ pussy clenched tight and wet around him.

“S-sorry, I didn’t catch that. W-what were you saying?” He grinned through his breathlessness, delighted at finally being able to have the upper hand. Edge glared at him, tugging uselessly at his restraints and trying to rock his body up, only for Sans to push him back down. Still, the other monster didn’t attempt to speak again and that was a win as far as Sans was concerned.

And every great achievement should be rewarded.

Sans looked down, eyeing the area where he and Edge were connected. The mix of blue and red made his soul twist in a lengthy, longing sort of way. His pussy had dripped wet blue magic down along the bones of Edge’s uncovered pelvis, stark against the whiteness of them. Edge’s own pre-come had mingled there as well. Sans reached his phalanges out to it, coating his fingers in the liquids and mixing them into a vibrant purple that he brought back up to his mouth. He gave the mixture a slow taste, licking it carefully off of every joint. He was well aware of Edge’s eyes on him throughout, gaze burning as it stayed fixed on his every movement.

When he reached back to coat his fingers once more, he gave a preparatory roll of his hips, making Edge moan and take a desperate, heavy breath. This time, he brought his phalanges up t his clit, circling the bundle of magic and wetting it with their combined slick. It felt dirty and disgusting in the best of ways, making him shiver as Edge gave him another heated look, eyelights flaring with barely disguised desire.

He lifted his hips up and waited just the briefest moment before sinking back down, fingers working quickly to help build his magic. When he caught Edge’s gaze again, he held it and a moment of understanding passed between them. This time, when Edge slammed his hips up to meet Sans as he sank back down, he didn’t stop the other skeleton, instead enjoying the rough, hard way that long cock filled him up.

Sans continued to bounce on Edge, rubbing at himself and watching with a lidded gaze as the skeleton beneath continued to quietly pant and exert himself, twisting in his bonds. The sight was amazing—the flush over Edge’s bones a striking look on someone usually so proud and composed. He shoved his hip down harder and grinned weakly at the way Edge moaned brokenly at the feeling.

Edge glared at him, thrusting back so hard that it had Sans gasping, phalanges slipping over his clit and making him shudder as his impending orgasm grew closer and closer.

“Hahh, come on, Edge,” Sans taunted, rubbing furiously over his magic and trying to keep his voice from wavering as he met the skeleton’s forceful thrusts over and over again, “Nothing to say anymore?”

But it seemed that Edge was far beyond hearing now. One look at him showed that he was close, likely not far behind Sans himself. He was sweating now, the effort of pounding into Sans likely difficult due to the way he was still tied up. Sans decided to have mercy on him.

He pulled his hand away from his clit and grabbed tight onto Edge’s hips instead. The monster looked up at him, confused, but the expression quickly morphed into understanding as Sans purposefully rocked his hips.

“A-ahh…” Edge groaned, body starting to tense.

Sans gave him another wicked grin before starting to bounce himself on Edge’s lap in earnest. He let the skeleton’s cock penetrate him deeply, stretching against his walls and thrumming with the imminent pulse of release. Sans fucked himself on Edge’s dick with a frantic pace, relishing in the sweet, broken moans he procured from every downward thrust of his hips.

It didn’t take much more before Edge was coming, thick, hot liquid gushing into him. Sans fumbled at the feeling, the rush of sticky mess inside of him making his hips falter in their movement even as his still wet phalanges came back to stroke at his clit. He rubbed at himself faster and faster, still rocking his hips to milk Edge of his orgasm, moaning loud at the feeling of the thick length twitching and dripping inside of him.

When at last he came, his pussy clenched down hard at the softening dick inside of him and Edge groaned at the overstimulation, wincing and grinding his teeth down tight.

Sans continued to stroke his clit through his orgasm, panting and, for once, uncaring of that fact that the other monster was seeing him in such an exposed and weakened state. He felt tired and worn, but in that good way that make the exhaustion well worth it. When the aftershocks died down, he flopped forward onto Edge’s chest, soul pounding hard against his ribcage. He couldn’t be certain, but it felt like Edge’s soul was giving off a calming pulse of its own, thrumming close to his.

Sans shifted in his position, wanting to get closer to inspect Edge’s soul, but when he moved, a thick slop of liquid poured out of him and made him wince. He’d forgotten how messy sex could be. With a sigh, he pushed all thoughts of investigation aside and slid off of the bed.

First things first—he needed to go and clean himself off.

He was halfway to the door when a hoarse voice called out to him.

“W-wait!” Edge said, rough and patchy, “Surely you’re not just going to _leave_ me like this?”

Sans looked him over.

Edge lay there on his bed, completely filthy. There was come and sticky release coated all over his pelvis. His bones where they weren’t covered by his clothes were shiny with sweat. He was still tied up, looking more vulnerable that Sans had ever seen him before. Even the shy, unsure way he’d asked was largely unfamiliar to him.

And for the briefest of moments, Sans considered leaving him there.

Then, he sighed.

It wouldn’t be right to do that to him—not now when Edge was acting so heart wrenchingly unguarded. So, Sans returned to his side with a few brisk steps. He quickly made to undo the knots keeping him pinned.

It was an easy fix—one that Edge could’ve no doubt done himself if push came to shove, so Sans could only imagine he’d asked because he’d wanted to know where this now left them.

“Thanks.” Edge mumbled at him, rubbing at his wrists and then turning to give him a grateful nod.

“Don’t mention it.” Sans responded and found himself giving Edge a genuine smile in reassurance, still floating on the feel-good pulses in his soul.

He didn’t magically find Edge and his personality perfect all of the sudden—didn’t think he was as great as he was always boasting he was—but. Edge _did_ seem a little more tolerable now at the very least. Sans was willing to admit that he wasn’t completely awful and that perhaps he hadn’t given him enough credit for that at the start.

Maybe, just maybe, things would be easier between them from now on.

“I’m going to clean up and then go make some lunch. Would you like anything?” He asked, a peace offering in light of what they’ve gone through together.

“Ugh, not if _you’re_ making it,” Edge groaned, pulling a face at the very thought, “Remind me to teach you what proper food tastes like sometime.”

Or maybe not.

**Author's Note:**

> ~~this is completely unedited and i swear i'll come back to it later for a re-read and re-work so pls forgive my no doubt many glaring mistakes LOL~~


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